1. Field of the Disclosure
The present disclosure relates to a technique of transferring uplink data at high speed from a lower-network apparatus to a higher-network apparatus in a communication system constituted of the higher-network apparatus and the lower-network apparatus connected through an optical subscriber system (PON: Passive Optical Network).
2. Discussion of the Background Art
An optical subscriber system using a passive double star configuration has high economic efficiency and is widely used worldwide as a GE-PON system or a G-PON system, and a high-speed 10G-EPON system and an XG-PON system have also been studied.
FIGS. 1-1 and 2-1 show a configuration of a conventional optical communication system. The optical communication system is constituted of a higher-network apparatus 1, an optical line terminal (OLT) 2, an optical fiber section 3 constituted of an optical fiber 3F and an optical coupler 3C, optical network units (ONU) 4-1, 4-2, . . . , and 4-N, and lower-network apparatus 5-1, 5-2, . . . , and 5-N.
The OLT 2 is connected to the lower network of the higher-network apparatus 1. The ONUs 4-1, 4-2, . . . , and 4-N are connected respectively to higher network of the lower-network apparatus 5-1, 5-2, . . . , and 5-N. The optical fiber section 3 connects the OLT 2 to the ONUs 4-1, 4-2, . . . , and 4-N.
In the optical fiber section 3, a portion between the OLT 2 and the optical coupler 3C is shared by the ONUs 4-1, 4-2, . . . , and 4-N. Thus, in a downlink direction from the higher-network apparatus 1 to the lower-network apparatus 5, TDM (Time Division Multiplexing) communication is performed, and meanwhile, in an uplink direction from the lower-network apparatus 5 to the higher-network apparatus 1, TDMA (Time Division Multiple Access) communication is performed.
In the uplink direction, to prevent uplink data from the ONUs 4-1, 4-2, . . . , and 4-N from conflicting with each other and to suitably allocate a bandwidth to the ONUs 4-1, 4-2, . . . , and 4-N, a dynamic bandwidth allocation (DBA) technology is realized (see Non Patent Literature 1).
FIGS. 1-2 and 2-2 each show a time chart showing an uplink data transfer procedure in the conventional art. Each of the lower-network apparatus 5 transmits uplink data to each of the ONUs 4. Each of the ONUs 4 buffers the uplink data and notifies the OLT 2 of an uplink data amount as a Report packet.
The OLT 2 allocates a transmission time and a transmission permission amount of uplink data to each of the ONUs 4 based on the Report packet of each of the ONUs 4. The OLT 2 then notifies each of the ONUs 4 of the transmission time and the transmission permission amount of the uplink data as a Gate packet.
Each of the ONUs 4 transmits the uplink data to the OLT 2 based on the received Gate packet. Thus, the uplink data from each of the ONUs 4 can be efficiently transmitted to the OLT 2 based on a required bandwidth without conflicting with each other.